Admittance spectroscopy of Ge quantum dots in Si

Self-assembled Ge quantum dots (QDs) embedded in Si-Schottky diodes were studied using admittance spectroscopy. A sample with one layer of Ge QDs embedded in p-Si was grown on a p⁺-substrate by molecular beam epitaxy and was processed into a Schottky diode structure. Activation energies have been determined as a function of the external bias voltage, which shifts the Fermi level in the sample. Two discrete activation energies of 318 and 303 meV have been extracted in the region of high bias voltage. They are identified as single and double charged QD ground state which is split up by a Coulomb charging energy. At approximately 40 meV lower activation energies several discrete levels attributed to excited dot states with a smaller energy separation of typical 5 meV are observed.